This invention relates to a current supply arrangement comprising a power transistor, which is driven by a control transistor and whose switching path is located each time between a terminal of an uncontrolled input direct voltage and a terminal of a controlled supply voltage, a current measuring resistor, a first control amplifier which drives the control transistor through a first electrode and compares a voltage to be derived from the supply voltage with a first reference voltage, and a second control amplifier which compares a measuring voltage to be derived at the current measuring resistor with a second reference voltage.
The operation of electronic circuits requires direct voltages at which a desired voltage value is maintained within a given tolerance range even with mains voltage fluctuations, load current fluctuations and temperature fluctuations. For these reasons, a direct voltage obtained, for example, by rectification from the mains voltage is not directly suitable. The operating voltage for electronic circuits, but it must be stabilized and smoothed by a following voltage control and current limitation means.
A current supply arrangement of the kind mentioned in the opening paragraph is known from U.S. patent Ser. No. 4,346,342. In this apparatus the voltage control means comprise a first control amplifier, which compares a voltage applied to the inverting input and obtained at the tapping point of a voltage divider on the output side with a reference voltage applied to the non-inverting input. The output of the first control amplifier is connected to the base of the control transistor. The current limitation means are constituted by a second control amplifier, which compares a measuring voltage to be derived at the current measuring resistor with a second reference voltage. The output of the second control amplifier is connected through a diode also to the base of the control transistor, while the emitter of the control transistor is connected through a resistor to a reference potential. Thus, the base of the control transistor is driven both by the first control amplifier for voltage control and by the second control amplifier for current limitation. Moreover, the reference voltages of the two control amplifiers are obtained from two separated reference voltages.